Indirectly heated cathode



Dec. 8, 1964 P. P. COPPOLA 3,160,780

INDIRECTLY HEATED CATHODE Original Filed Aug. 12, 1955 4 Eqi 12 INVEN TOR PA TRICK .P COPPOLA United States Patent 3,160,780 INDIRECTLY HEATED CATHODE Patrick P. Coppola, Fayetteville, N .Y., assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 527,952, Aug. 12,

1955. This application Jan. 17, 1961, Ser. No. 83,862 6 Claims. (61. 313-446) The invention relates to an indirectly heated cathode and in particular to an indirectly heated dispenser cathode.

This application is a continuation of application Serial No. 527,952, filed August 12, 1955, now abandoned.

In a dispensercathode, the emissive surface is continually supplied with alkaline earth metal, such as barium, from a supply of an alkaline earth material'contained in one or more cavities in the body by reaction with the refractory metal constituting the body. Thus, in certain types of dispenser cathodes, not only is the barium metal furnished to the emissive surface but also to surfaces of the body from which no emission is desired. Moreover, in one form of dispenser cathode in which the alkaline earth material is distributed in the pores of a porous refractory metal body and which is raised to the operating temperature by a separate heating element, undesired emission may take place between the cathode and heating element unless provision is made to prevent such emission.

It is a principal object of the invention to provide an indirectly heated dispenser cathode in which emission between the cathode and the heating element is prevented.

It is a further object of the invention to provide an indirectly heated dispenser cathode of simple, inexpensive construction.

It is a still further object of the invention to provide an indirectly heated dispenser cathode in which emission between the cathode and heating element is prevented and which is simple and easy to fabricate.

secured to a tubular refractory metal housing for a heating element. This refractory metal member may be plateor cup-shaped and serves to support the electronemissi-ve element and prevent emission between the cathode and the heating element. The electron-emissive element preferably comprises a pressed and sintered mixture of tungsten, or an alloy of tungsten and molybdenum, and a fused mixture of at least 60% by weight of barium oxide and aluminum oxide. However, use may be made of other refractory metals such as molybdenum, tantalum and hafnium and alloys of those metals as well as other alkaline earth materials such as fused mixtures of alkaline earth oxides with acidforming oxides such as silicon dioxide, beryllium oxide and boric oxide.

For a more complete understanding of the invention, reference is made to the accompanying drawing in which:

FIGS. 1a and lb show One embodiment of a cathode according to the invention;

"ice

ping. If desired, theoverlapped edges may be welded using a tantalum flux or an inert atmosphere but this step may be omitted. This tube houses a heating element 2 and supports at one end an electron-emissive wafer 3 mounted on a molybdenum plate 4 (shown in greater detail in FIG. lb).

The electron-emissive wafer 3 is formed by mixing together about 90% by weight of a 25% W% Mo alloy and 10% by weight of a fused mixture of about 5 moles of BaO and 2 moles of A1 0 This mixture is then pressed and sintered at about 1370 C. for about 20 minutes to form a coherent body and the temperature raised for about 20 seconds to the melting point of the fused mixture of BaO and A1 0 (about l650-1750 C.) brightness in order to degas the composition. Alternately, this water can be formed as described in US. Patent 2,700,000 to R. Levi et al.

In order tosecurely attach the electron-emissive water 3 to support 4, it is preferred to Weld the element to the disc. Alternatively, the pressed mixture of tungsten and fused mixture of barium oxide and aluminum oxide may be placed on the molybdenum disc and the bodies sintered together to form a unitary assembly.

The molybdenum disc 4 is then welded, as described above to the walls of tube 1, for example, by passing an electric current of suificient density to produce localized heating without unduly heating the emissive body.

As will be evident, the plate 4 effectively prevents any emission from the wafer 3 to the heating element 2.

Instead of using a plate-shaped support, the electronemissive element 3 may be mounted in a cup-shaped support 5, as shown in FIGS. 2a and 2b, having a rim 6 adapted to be secured to the end of the molybdenum tube 1.

The cup-shaped support may also be secured within the molybdenum tube, as shown in FIGS. 3a and 3b, by peening over the ends 7 of the tube and the edge of the cup and by providing a reentrant portion 8 in the tube below the cup.

As a further alternative, theemissive 'body may have a portion 9 extending beyond the cup, the cup being recessed in the molybdenum tube as shown in FIGS. 4a and 7 A simple die structure for fabricating the cathode shown in FIGS. 3:: and 3b and FIGS. 4a and 4b is shown in FIG. 5. The cup-shaped member is placed in a cylindrical die 10 provided with a cupped pin 11 to seat the body while pressing. A measured quantity of the emitter mixture 12 is placed in the die above the cup and the mixture pressed into the cup by pressing pin 13.

FIG. 6 shows a similar die for forming an emitter element of the type shown in FIG. 2b. The cupped pin 11 is designed, in this case, to receive a rimmed. cup 5.

After pressing, the emitter bodies are sintered in the aforesaid manner. As a resultof this sintering, 'a tight bond is obtained between the emitter and the cup which insures better heat transfer to the emitter, less evaporation of Ba and BaO from the sides of the cup and less likelihood of fracturing or chipping the emitter body. While the invention has thus been described with referand sintered metallic materialheld in the'said tube, a

projection from the face ofthe said block formed of active material which is a compressed and sintered mass of tungsten powder mixed with thermionically active ma terial, and a metal shield enclosing the said block with the end of the said projection being spaced from said metal shield.

3. A thermionic cathode comprising a metal tube adapted to house a cathode heater, ablock of compacted 7 and sintered metallic material heldin the said tube, a

projection from the face of the said block formed of ace tive material which is a compressed and sintered mass of a tungsten-molybdenum alloy powder mixed with thermi onically active material, and a metal shield enclosing the said block with the end of the said projection being spaced from said metal shield.

4. A thermionic cathode comprising a metal tube adapted to house a cathode heater, a block of compacted and sintered metallic material held in the said tube, a projection from the face of the said block formed of active material which is a compressed and sintered mass of refractory metal powder mixed with thermionically active material composed of a fused mixture of barium oxide and, aluminum oxide, and a metal shield enclosing the said block with the end of the said projection being I spaced from said metal shield.

5. A thermionic cathode comprising a metal tube adapted to house a cathode heater, a block of compacted and sintered metallic material held in the said tube, a projection from the face of the said block formed of active 10 material which is acompress ed and sintered mass of refractory metal powder mixed with thermionically active material composed of a fused mixture of at least by weight of barium oxide and aluminum oxide, and a metal shield enclosing the said block with the end of the said projection being spaced from said metal shield.

6. A thermionic cathode comprising a metal tube adapted to house a cathode heater, a block of compacted and sintered'metallic material held in the said tube, a projection from the face of the said block formed of active material which is a compressed and sintered mass of'refractory metal'powder mixed with thermionically active material, and a cup-shaped metal shield enclosing the Levi et al Jan. 18, 1955 2,741,717 Katz Apr. 10, 1956 3,013,171 Beck Dec. 12, 1961 

1. A THERMIONIC CATHODE COMPRISING A METAL TUBE ADAPTED TO HOUSE A CATHODE HEATER, A BLOCK OF COMPACTED AND SINTERED METALLIC MATERIAL HELD IN THE SAID TUBE, A PROJECTION FROM THE FACE OF THE SAID BLOCK FORMED OF ACTIVE MATERIAL WHICH IS A COMPRESSED AND SINTERED MASS OF REFRACTORY METAL POWDER MIXED WITH THERMIONICALLY ACTIVE MATERIAL, AND A METAL SHIELD ENCLOSING THE SAID BLOCK WITH THE END OF THE SAID PROJECTION BEING SPACED FROM SAID METAL SHIELD. 